A lone gunman inside the Mandalay Bay Resort and Casino opened fire Sunday night on attendees of the Route 91 Harvest Festival, a three-day, country music event, according to the New York Times. As of Monday afternoon, at least 58 people were reported dead, and more than 500 others taken to local hospitals. Jason Aldean was the final performer Sunday night around 10 p.m. when gunfire descended on the crowd from above. Videos show the country singer halting mid-song as gunfire sounds in the background.

Las Vegas police identified the shooter as Stephen Paddock, 64, of Mesquite, Nevada, about 80 miles northeast of Las Vegas near the Arizona border. The Associated Press reports Paddock opened fire from the 32nd floor of the hotel, but Paddock was already dead by the time SWAT teams stormed his room. Authorities have not yet determined a motive, but believe Paddock acted as a "lone wolf."

The Las Vegas massacre eclipses the mass shooting in Orlando in June 2016 as the deadliest in modern U.S. history; the attack at Pulse nightclub left 49 dead and 58 wounded. President Donald Trump tweeted, "My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!" The president plans to visit Las Vegas on Wednesday.

Mandalay Bay sits at the south end of the famed Las Vegas Strip, close to the airport, and the complex also includes The Delano hotel and the Four Seasons Las Vegas. Sunday's attack briefly halted flights in and out of Las Vegas's McCarran International Airport, but by 3 a.m. Monday, regular service had resumed, according to USA Today.

"People are under the impression they go into a casino and they're safe because it's a secure place with 2,000 or 3,000 surveillance cameras," Del Marva says. "It's only in the gaming room. I don't see how you prevent it. The masses of people that come through there, there's no way to screen everybody."

A threat assessment expert told Fox Business that she foresees casinos tightening security following Sunday's attack, beefing up outdoor security at venues and potentially installing metal detectors. But Del Marva says metal detectors would be tough to implement, just given the sheer volume of people flowing through each resort every day.

"If you go to Bellagio, at any time, you can see 200 too 300 people checking in. How do you screen something like that?" Del Marva tells Traveler. "Tom Brokaw was talking [on NBC] about metal detectors, but that's impossible. It'll create chaos. The check-in process will be ridiculous."

Del Marva says that while Las Vegas hotels and casinos might see a temporary downtick in business after the attack, concerts and large venues will experience a more profound impact.

"People are going to stay away from concerts," he says. "Going to large venues, where you're stuck there. If you start to run out, people get stampeded, and more are gonna be killed."

In hindsight, Del Marva also doesn't believe there's much Mandalay Bay security could have done.

"If I were retained by a casino to tell them what to do to prevent this, I wouldn't know what to tell them," he says.

This is a developing story. Please continue to check back for more updates.